The Nature of the 'Mono' Ligand Complexes of Iron(II) with 1,10-Phenanthroline-2-carbothioamide and 2,2´-Bipyridine-6-carbothioamide. Low-Spin Iron(II) and High-Spin Iron(III) Systems

Abstract

Interaction of 2,2′-bipyridine-6-carbothioamide (bta) with iron(II) chloride leads to three different products: [Fe(bta)₂]Cl₂·H₂O, [Fe(bta)₂][FeCl₄] and an apparently ‘mono’-ligand complex analogous to the previously described Fe(pta)Cl₂·H₂O (pta = 1,10-phenanthroline-2-carbothioamide). Electronic and Mössbauer spectroscopic data show that all three complexes of bta contain the [Fe(bta)₂]²⁺ cation. The Mössbauer spectra, together with the magnetic properties, indicate that the [Cl₃Fe–O–FeCl₃]^2– ion is associated with the cation in the ‘mono’ complex which is formulated as [Fe(bta)₂]₂[Cl₃Fe–O–FeCl₃]Cl₂·3H₂O. The unusual temperature dependence of the Mössbauer spectrum, and the magnetism of this complex, arises from the presence of different iron sites, one being low-spin iron(II) and the other high-spin iron(III). Two of the latter are antiferromagnetically coupled in the oxobridged anion. 2,2′-Bipyridine-6-carboxamide (bca) yields an iron(II) mono-ligand derivative, Fe(bca)Cl₂·H₂O, which is a simple high-spin paramagnet.